Homeless advocacy groups are criticizing a move by Mayor Antonio Villaraigosa to ban tents from all Los Angeles city parks.

The City Council is expected to vote Tuesday on the new ordinance, which bans tents from parks during day and nighttime hours. The ordinance was requested by Villaraigosa and expands an existing law that bars camping in most city parks.

While the move is widely viewed an an effort to discourage Occupy L.A. protesters from returning to the City Hall lawn where they camped for two months, homeless advocates expressed disappointment.

"It just follows the mayor's continuing criminalization of the poor and protesters," said Becky Dennison, co-director of the Los Angeles Community Action Network. "Generally, people who sleep in tents have nowhere else to go."

Peggy Kennedy, a member of the human rights group Venice Justice Committee, questioned how the city would define the word "tent."

"I'm not a lawyer, but it sounds constitutionally vague," she said.

The ordinance was quickly drafted by the City Attorney's Office in response to a motion submitted last week by Councilman Richard Alarcón.

In writing the ordinance, attorneys sought to clarify between a tent and shade structures, and they studied the different items on web sites for legal clarification, Assistant City Attorney Valerie Flores said.

Umbrella or sun shade structures are allowed under the law, if they are open on all sides and no more than eight feet high and ten feet wide. Tents or any shelter that is not open on at least two sides would be banned.

"We don't want to have people confused about what they can and can't do," Flores said. "It all boils down to an issue of enforcement. Our goal is to have clarity."

Earlier this year, the city sought to reduce nighttime operating hours at the City Hall park, but they haven't yet decided what to do. Rules regarding park hours could come in a later ordinance, Flores said.

Villaraigosa's office did not return a request for comment by deadline.